A Guide to the 3 Types of eSignatures: SES, AES, and QES Defined

There are three primary types of electronic signatures, as defined by the European Union’s eIDAS regulation: Simple Electronic Signatures (SES), Advanced Electronic Signatures (AES), and Qualified Electronic Signatures (QES). These signatures are differentiated by their level of security, authentication, and legal validity. While SES is the most basic, a QES provides the highest level of assurance and is legally equivalent to a handwritten signature.

With a host of business benefits like increased efficiency, cost savings, and stronger security, electronic signatures play a powerful role in the digital transformation of many organizations.

Different types of eSignatures exist, each with distinct capabilities and use cases. Understanding each method will help you ensure you invest in the most secure and compliant solution for your business requirements.

Here is a simple guide to the three types of eSignatures, including their key differences and use cases, to help you make an informed decision.

eIDAS: The Legal Framework for eSignature Classification

The eIDAS regulation (Electronic Identification, Authentication and Trust Services) is the foundational legal framework in the European Union that governs electronic identification and trust services for digital transactions.

This regulation standardizes the legality of eSignatures across the EU, classifying them by the level of assurance, security, and legal weight they provide.

This regulation defines three distinct tiers of electronic signatures:

1. Simple Electronic Signature (SES)
2. Advanced Electronic Signature (AES)
3. Qualified Electronic Signature (QES)

Simple Electronic Signature (SES)

The Simple Electronic Signature (SES) is the most basic type of eSignature, offering the lowest level of security and legal assurance. An SES works by capturing the signer’s intent to agree to a document, but without a high degree of identity verification or security to protect the document from being altered.

It's primarily used for day-to-day signing requirements where the risk of a legal dispute is low. While it is legally valid, the burden of proof to demonstrate authenticity falls on the party relying on the signature.

Key Characteristics

• Low Assurance: Provides a basic level of consent without robust identity verification.
• Minimal Security: The signature itself is not cryptographically linked to the document, meaning it does not guarantee the document's integrity after signing.
• Ease of Use: It's the most convenient type of eSignature to create and use.

Common Examples & Use Cases

• A scanned image of a handwritten signature.
• A signature drawn on a desktop or mobile screen.
• A "click-to-sign" or "I accept" button on a website.
• Signing internal HR documents like expense reports or vacation requests.
• Acknowledging receipt of company policies.
• Non-disclosure agreements (NDAs) or low-risk commercial agreements.

For a deeper dive into the specific legality of Simple Electronic Signatures in different jurisdictions, see our Ultimate Guide to Electronic Signatures eBook.

Advanced Electronic Signature (AES)

An Advanced Electronic Signature (AES) is a legally recognized eSignature that provides a higher level of security and authentication than an SES. Defined by the eIDAS regulation, an AES must meet specific technical requirements to ensure a high degree of signer identity verification and document integrity.

This type of signature is ideal for business processes that require greater confidence in the signer's identity and proof that the document has not been altered after signing.

Key Characteristics

• Uniquely Linked to the Signer: The signature is created using data that is exclusively under the signer’s control, ensuring a direct link between the signer and the signed document.
• Tamper-Evident: The signature is cryptographically linked to the document, which creates a tamper-evident seal. Any changes made to the document after it has been signed will invalidate the signature, providing proof of the document's integrity.
• Increased Legal Assurance: The signer’s identity is verified and tied to the signature, reducing the legal risk and burden of proof compared to a Simple Electronic Signature.

Common Use Cases

• HR Documents: Employee onboarding, employment contracts, and internal policy agreements.
• Commercial Contracts: Sales agreements, purchase orders, and invoices where a medium level of assurance is required.
• Financial Services: Opening new customer accounts or authorizing financial transactions.
• Legal Documents: Non-disclosure agreements (NDAs) and other legal agreements that require greater security than an SES.

Qualified Electronic Signature (QES)

A Qualified Electronic Signature (QES) represents the highest level of security and legal validity for eSignatures, as defined by the eIDAS regulation. A QES is the only type of eSignature that is legally equivalent to a handwritten signature and carries a legal presumption of validity across all European Union member states. This means the burden of proof falls on the party attempting to dispute the signature.

A QES is created using a qualified certificate issued by a Qualified Trust Service Provider (QTSP). QTSPs are rigorously audited and accredited providers, ensuring the highest standards of security and reliability.

Key Characteristics

• Legally Equivalent to a Handwritten Signature: A QES holds the same legal standing as a physical, wet-ink signature.
• Highest Level of Security and Authentication: The identity of the signer is verified in person or through an equivalent remote process, and the signature is created by a qualified electronic signature creation device.
• Qualified Trust Service Provider (QTSP): The qualified certificate that binds the signer's identity to the signature must be issued by a QTSP on the EU Trust List.
• Burden of Proof: A QES is presumed valid. If its authenticity is challenged, the party disputing the signature is responsible for proving it is not valid.

Common Use Cases

• High-Value Transactions: Signing purchase contracts for real estate or leasing agreements.
• Corporate Governance: Board resolutions, shareholder agreements, and other official company documents.
• Legal & Public Sector: Documents requiring a notarized or sworn signature, and interactions with government bodies.
• Financial & Banking: High-value loan applications, mortgages, and other formal banking agreements.

A Comparison of eSignature Types: SES vs. AES vs. QES

The primary difference between the three types of electronic signatures is the level of security and legal assurance they provide.

This is determined by how each signature addresses four key elements: identity, authenticity, integrity, and authentication.

The following table provides a detailed breakdown.

Choosing the Right eSignature Method for Your Business

Choosing the right eSignature method requires a strategic evaluation of your specific business needs and global regulatory requirements. By answering these key questions, you can determine the level of assurance and compliance necessary for your transactions.

What is the business value you need to achieve?

Define the immediate and long-term goals of implementing eSignatures. While your current needs may be basic, consider how your digital transformation roadmap and growth plans might require higher levels of security and legal compliance in the future.

• Low-Value Needs: For basic, internal documents, a Simple Electronic Signature (SES) may be sufficient.
• Growing Needs: As your business scales and handles more critical documents, an Advanced Electronic Signature (AES) offers a necessary upgrade in security and authentication.
• High-Value Needs: For legal and highly regulated transactions, a Qualified Electronic Signature (QES) ensures the highest level of legal validity and protection.

What are the use cases within your existing workflows?

Analyze your current workflows to identify where eSignatures can add value. The appropriate signature type depends heavily on the context and importance of the documents being signed.

• Day-to-day Tasks: For routine, low-risk activities like acknowledging company policies or approving expense reports, an SES is often the most efficient option.
• Standard Business Operations: For transactions like sales contracts or onboarding new employees, an AES provides the necessary security and legal defensibility.
• High-Stakes Projects: For high-value, cross-border, or legally complex projects (e.g., real estate agreements, mergers and acquisitions), a QES is typically required to meet strict regulatory and legal standards.

What are your compliance and security requirements?

The legal and regulatory environment is a primary factor in your choice. The risk associated with a transaction dictates the required level of security and authentication.

• Low-Risk Documents: For documents with minimal legal exposure, an SES is typically adequate.
• Industry Standards: In regulated industries like finance, healthcare, and law, an AES or QES is often mandated to comply with specific data protection and eSignature laws (e.g., eIDAS, ESIGN Act).
• Global Transactions: For international or cross-border agreements, a QES offers a legal presumption of validity that simplifies enforcement and reduces legal risk across multiple jurisdictions.

Once you have a clear understanding of your requirements, selecting an eSignature vendor becomes a straightforward process of matching their offerings to your specific needs.

FAQs About the Different Types of eSignatures

What is the difference between an electronic signature and a digital signature?

An electronic signature is a broad legal term for any electronic process that indicates a person's acceptance of a document. A digital signature, however, is a specific type of electronic signature that uses a cryptographic technology to secure a document and verify the signer's identity. All digital signatures are electronic signatures, but not all electronic signatures are digital signatures.

Are eSignatures legally binding?

Yes, in many jurisdictions worldwide (including the U.S. and EU), eSignatures are legally binding and admissible in court. In the U.S., the ESIGN Act and the Uniform Electronic Transactions Act (UETA — adopted by 49 states; New York uses the Electronic Signatures and Records Act) provide the legal framework. In the European Union, the eIDAS regulation governs their legal standing.

Is a QES legally equivalent to a handwritten signature?

Yes. Under the eIDAS regulation, a Qualified Electronic Signature (QES) is the only type of eSignature that holds the same legal value as a handwritten signature. It is presumed to be valid in all EU member states.

How do SES, AES, and QES differ in terms of security?

The three eSignature types are classified by their level of security:

• SES provides the lowest level of security and does not verify the signer's identity.
• AES offers a higher level of security by uniquely linking the signature to the signer, ensuring the signer can be identified, and making any post-signing change detectable.
• QES provides the highest level of security, requiring strict identity verification by a Qualified Trust Service Provider (QTSP).

What is the role of a Qualified Trust Service Provider (QTSP)?

A Qualified Trust Service Provider (QTSP) is a highly regulated and accredited entity that is responsible for verifying a signer's identity and issuing the qualified certificates necessary to create a QES. Their role is to ensure the integrity and legal validity of the signature, making them a crucial part of the QES process.

Do I always need a QES for my documents?

No. The required level of eSignature depends on the legal requirements and the risk associated with the document. While a QES is legally equivalent to a handwritten signature, an SES is sufficient for low-risk, day-to-day documents, and an AES is often a great choice for standard business contracts.

Can an SES be used in court?

Yes, an SES can be used as evidence in court. However, unlike a QES which has a legal presumption of validity, the party relying on the SES would have the burden of proof to demonstrate its authenticity and the signer's intent to be bound by the document.

How can I verify an eSignature?

Verification depends on the type of eSignature:

• Advanced Electronic Signatures (AES) and Qualified Electronic Signatures (QES) are verified using cryptographic methods. This means checking the signature’s cryptographic properties (e.g., public-key validation), confirming that the certificate is valid and issued by a trusted provider, and ensuring that the document has not been altered since signing.
• All eSignatures—including Simple Electronic Signatures (SES)—should be supported by an audit trail. This typically records signing events, timestamps, IP addresses, email addresses, and explicit consent confirmations. The audit trail serves as supplementary evidence in case the authenticity of the signature is challenged.

Example:
If you receive a QES-signed PDF, you can open it in a trusted PDF viewer that supports signature validation (e.g., Adobe Acrobat, Nitro PDF Pro). The viewer will check the certificate’s trust status, verify the signature’s integrity, and display whether it is valid. Alongside this, your eSignature platform should provide an audit log showing the signer’s verified identity, when they signed, and the method used to authenticate them.

What is the eIDAS regulation?

The eIDAS regulation is the European Union's legal framework for electronic identification and trust services in the EU single market. It established a standard for the legal status of eSignatures, e-seals, and other electronic trust services, ensuring that they are legally valid and enforceable across all EU member states.

Drive Business Results with Nitro Sign

Understanding the different types of eSignatures is the first step. Whether you need to sign a simple internal form or a high-value real estate agreement, Nitro Sign can help you navigate your eSignature journey and implement a solution that's right for your business.

Talk to our sales team today to get started.